Organic semiconductors have attracted considerable interest in the last years as potential substitutes for inorganic semiconductors, which are more expensive and difficult to process. Furthermore, organic semiconductors are more flexible and lighter which opens a whole new area of wearable electronics. Of particular interest are organic semiconductors that are solution processable since they are amenable for large scale production and large area applications.
The huge research effort made recently on the development of these materials and their processing has raised the prospect of commercially using organic semiconductors in applications such as organic field-effect transistors (OFETs), organic light-emitting diodes (OLEDs), organic photovoltaic solar cells or organic thermoelectric devices (OTEGs).
Semiconductive materials can be classified in p-type or n-type semiconductors depending if the majority charge carriers are holes or electrons, respectively. Despite the fact that p-type organic semiconductors have achieved great advancement, their n-type counterparts are lagging behind in performance. Doping processes to obtain higher performance n-type organic semiconductors are difficult or make them unamenable to solution-processing. This unfortunate fact has delayed progress on organic semiconductor devices including OFETs, OLEDs, organic photovoltaic solar cells and OTEGs, which require both n-type and p-type materials. Therefore, there is a need for the development of new n-type materials that allow large scale production to improve the performance of organic devices.
In this disclosure, a very simple water-processable n-type semiconductor is shown. This semiconductor comprises polyvinylpyrrolidone (PVP) and carbon nanotubes (CNTs) dispersed in water formulations, into which small amounts of poly(ethyleneimine) (PEI) are added to improve semiconducting properties. The formulations are prepared by mixing the desired amount of PVP, CNTs, PEI and water, following by high power sonication until a good level of dispersion is achieved.